<tr class="marca_row">
  <% fields_for "concurso[marcas_attributes][]", marca do |v|%>
    <td><%= v.collection_select(:marca_id, @marcas, :id, :nombre, {:include_blank => true}) %></td>
    <td><%= link_to_function "Quitar", "$(this).up('.marca_row').remove()" %></td>
  <% end %>
</tr>